Exercise machines and apparatus using hydraulic cylinders as a resistance or power source have existed for some time. Generally, these prior art methods are limited by design and physics in terms of restricted direction of resistance and speed of response.
The exercise modality for most exercising equipment harnessing hydraulic force is aimed at building strength, muscle mass, and muscle tone. For example, hydraulic dampers have been used to generate a resistance force. This force is generally passive and only provides either a fixed or variable resistance force. An example of such a passive exercise machine is found in U.S. Pat. No. 5,527,251 to Davis which provides for a bidirectional, adjustable resistance exercise machine. Another exercise application for a hydraulic cylinder is found in U.S. Pat. No. 5,803,879 to Huang for a double-acting hydraulic cylinder that delivers a variable resistance to provide a smooth movement and resistance in two directions (e.g. back and forth). Both of these prior art exercise devices are passive devices.
A more ambitious method for an exercise machine using hydraulic forces is found in U.S. Pat. No. 4,865,315 to Paterson et. al. This prior art device provides a manual mode where the user selects a concentric and eccentric force, a pyramid mode where the user selects an automatic increasing progression of concentric and eccentric force, and a maximum strength exercise mode where the user applies maximal muscular force. In this device, a computer controls the hydraulic force and pressures in the hydraulic system to deliver the desired exercise modality. Another exercise device is found in U.S. Pat. No. 6,413,195 to Barzelay. This application provides for either a resistance type operation or a velocity type operation controlled by a computer to deliver a push-pull mode of operation. Another application harnessing hydraulic forces for athletic training is U.S. Pat. No. 3,062,548 to Foster, which discloses a training cart with hydraulic pump to generate a passive resistance to movement.
For the most part, these prior art applications use hydraulic dampers or cylinders to deliver brute force resistance and generally lack dynamic control of the generated resistance. As such, these prior art exercise machines are useful for traditional anaerobic strength training. These conventional applications usually impose higher forces as velocity increases, and systems employing conventional hydraulic cylinders produce high friction forces, rigidity, and penalize high speed exercise.
Any hydraulic cylinder's speed of movement is limited to the velocity of the fluid within the cylinder. This velocity is restricted by the smallest orifice in the system. Most traditional passive exercise cylinder use restrictive orifices to generate exercise forces. While this approach generates exercise forces, these devices are very velocity sensitive and are limited to use in a narrow speed range. Active hydraulic cylinder devices typically have ports and valving that are the limiting factor on speed of movement. Because a typical positive displacement hydraulic cylinder has multiple hydraulic shaft and piston seals, it generates substantial friction forces from these seals. These forces vary with higher initial breakout forces and direction and velocity sensitive dynamic forces.
A need exists for a force generation device for exercise machine applications directed at developing the quick response muscles needed for athletic success. Such a device needs to allow training modalities with dynamic, active responses for increasing agility along with rapidly controllable forces appropriate to the athletic or rehabilitation need. This type of training would be valuable for applications in exercise machines used by athletes training in football, basketball, baseball, track, rowing, as well as for rehabilitation.